Im handing in my notice at work tomorrow. Im keeping the letter of resignation short and sweet, but i just have one question i hope someone can answer for me...

Is the "effective date of resignation" the last date you will work or the first day you will no longer be employed by them?

Ive been googling the question like crazy and still cant find a clear answer.

I would have thought it is the date you hand over the letter.
Your notice period starts from that date.

Just say one week (or whatever your notice period is), effective from 12th March 2013, meaning you will finish next Tuesday 19th March 2013, for example.

Effective date of resignation is the date your resignation takes effect. It is the day your employment ends, rather than the day you hand your notice in.

Generally when I've handed in my resignation, I've been very specific and said I'd work my 1 months notice (or whatever length of time) and my last day of employment would be... xx/xx/xx

Everyone knows exactly where they stand then.